You got a major, major GPU performance problem there. It is very obvious that your graphics card cannot keep up with the stuff it gets sent. I just had a look at a graphics card benchmarking site and the card you have is equivalent to a lower mid-level card like the Geforce 8600 from 12 years ago. I had such a thing from 2007 to 2012 and this had massive performance issues on wide open maps, like Hellcore's "Hobbs End Horror" with fps rates around 20. On the Geforce 550Ti I got afterward that map runs with 160 fps from the most problematic locations (obviously also on a faster computer.) I guess your system is roughly comparable to the one I had back then.
What do you get when you run with '-glversion 2'? That will disable the shaders which on such slow hardware might actually help. As a target for optimization such slow hardware won't do much good, though. The problems you fix will never appear on faster hardware.